1. Field of the Invention
The present invention is directed to a system and method for the forming of local features in, and/or accomplishing the localized joining of sheet materials of various composition, by the contacting of the materials with a high-velocity projectile. The system and method The area of the sheet material to be formed is placed over a forming die having a cavity of desired shape. A preferably deformable projectile is then propelled into the area of the sheet material to be formed, such that a portion of the material is driven into the forming die. The system and method of the present invention may be used to form particular features in the sheet material, to join two or more sheets of material, or to connect a sheet of material to a secondary component. When more than one material is used, the materials may be of like composition or, alternatively, the system and method of the present invention may be employed to join dissimilar materials.
2. Background
Many products are manufactured from metallic or other sheet materials, wherein the products require the forming of particular, localized features at certain locations thereon. Similarly, there are many products whose manufacture requires the attachment of one or more secondary components to a sheet material at one or several localized sites. In a typical attachment process, a secondary component may be locally joined to a sheet material by forcing a portion of the material through an opening in the component and into a subjacent cavity, whereby the shape of a cavity into which the material is forced thereafter causes the material to expand outwardly, mechanically connecting the sheet of material and the second component. Two or more sheet materials may also be locally joined by employing the system and method of the present invention. Manufacturers of aluminum cans, and automotive and aerospace products, for example, commonly employ systems and methods for effecting localized feature forming, the attachment of secondary components, and/or the localized joining of metallic materials. Such a system and method may be used, for example, to attach a pull tab to the top of a can for containing a beverage or a foodstuff.
There are known systems for providing localized feature forming and/or the localized joining of metallic materials. The most commonly employed system is likely that of the punch and die. In a punch and die system, one or more sheets of metallic material are placed between a cavity containing die and a corresponding punch. The punch and die are typically disposed on opposing portions of a forming machine, such as a hydraulic press or similar device. The forming machine causes the punch and die to come together, whereby the punch forces a portion of the metallic material into the die cavity—producing a formed feature in the material. Similarly, two or more sheet materials may be placed over a die having a properly shaped cavity, such that when the punch forces the materials into the cavity each of the materials is caused to bulge outwardly, thereby effectively affixing each material to the other by way of an interlocking shape. Such a process of mechanically interlocking the two or more materials is commonly referred to as spot clinching. It is also possible to attach a secondary component to a sheet material by using the punch to force a portion of the material through an aperture in the secondary component, and thereafter causing the material to expand outwardly beyond the circumference of the aperture—thereby effectively locking the secondary component to the sheet material. While the punch and die method of feature forming and localized joining is likely the most common method in use, it is not without limitations and problems. This process is generally limited to high ductility materials, because the operation of the punch and die generates a high shear force and may also cause a significant thinning of the materials to which it is applied. Such a mechanical process also typically requires a large structure for supporting the materials to be formed or joined, as well as a large force generating device, such as the hydraulic press mentioned above, to drive the punch into the die. In mechanical joining processes, the materials are also limited to joining by interlocking of the shapes produced by the punch and die, as a metallurgical bond between the materials cannot be developed thereby.
Electromagnetic forming has been used to generate high-velocity movement of a sheet, which can then be used to impart a shape to both entire metal sheets, and to smaller, localized features within a metal sheet. While electromagnetic forming has proven effective for use in forming large features, it is typically less effective when utilized to form smaller, localized features. The forming of localized features often requires the application of very high and localized forces. In such cases, process efficiency suffers, and small robust actuators are quite difficult to fabricate. Consequently, because it is very difficult to focus sufficient electromagnetic energy on a small surface area, it is generally not practical to use an electromagnetic forming process in this manner.
Localized high explosives have been used for some time to join primarily dissimilar metallic components. Typically, one component is situated at a slight distance from the other component, so that an explosive charge can be used to drive the components into contact with one another. The explosive charge causes the components to collide at a sufficient velocity and angle to form a metallurgical bond therebetween. Explosive welding is commonly used to create sealed joints, such as vacuum joints, between metals such as aluminum, copper and stainless steel. Other uses for explosive welding may include the placement of a cladding onto a steel substrate, and the joining of aluminum to low-expansion metals in the electronics industry. Explosive welding is not typically used to form localized features or to join thin metallic sheets.
Ultrasonic or friction welding has also been used to join metallic and non-metallic components. Such methods involve placing the components into contact and causing movement along the joint interface located therebetween. Commonly, a friction weld is generated by rotating one component against a fixed second component under pressure. In this manner, sufficient frictional heat can be produced between the components such that at least one of the components can become plastic at the joint interface. When the rotational motion is halted, the components become physically bonded together. Friction welding also generally requires that at least one of the components be circular at the joint interface. Friction welding cannot be used to form localized features, and also cannot be used to join sheets of metallic materials in localized areas.
Hyper-pressure water jet pulses have recently been proposed to accomplish the bonding of aluminum components. In this method, a hyper-pressure pulse is developed by directing a high-pressure water jet pulse through a tapered nozzle to further increase its acceleration and pressure. Aluminum components to be joined are placed on an assembly fixture where they can be contacted with the hyper pressure water jet pulse. The hyper pressure water jet pulse can be used to cause a mechanical interlocking of the components and, if the stagnation pressure of the pulse is sufficiently high, may cause a plastic deformation of the components. This technique requires an ultrahigh-pressure pumping system to generate hyper pressure water jet pulses. This technique also requires the use of a manipulator, such as a robotic arm, to place the water jet nozzle substantially against the materials to be formed or joined.
While it can be seen from the foregoing that there are various systems and methods for providing localized feature forming and joining of materials, some of which can be used to join dissimilar materials, there remains a need for a system and method that can produce localized features that cannot effectively be produced by these known methods. For example, it is desirable to satisfactorily produce localized features that currently typically result in a tearing or excessive thinning of the material or materials involved. There also remains a need for a system and method of efficiently producing a localized joining of multiple sheets of material, wherein more than a mechanical bond is created therebetween, and/or where the joining may be accomplished at arbitrary points over a large surface area. For example, to increase the strength of the joint created between the materials, it is desirable that a metallurgical bond be created, such as by causing the materials to become plastic in the joint area. Such a method may be used to join similar or dissimilar materials.